Theres nothing about the maximum wage that makes it more symptomatic of 'the politics of envy' more than any sort of taxation that targets the super rich. Is a 60% tax rate 'the politics of envy'?
Why do you think a maximum wage 'do nothing to help the poor'? In 2009 a couple of LSE professors published a book called The Spirit Level demonstrating that there was a direct correlation between reducing the gap between rich and poor and societal gains in health, education, happiness indicators etc affecting all strata of society, rich and poor. The Spirit Levels findings were taken on board and referenced by Milibands Labour and the Tories at the last election, so its not the preserve of any one political point of view. In simple terms, you need to narrow the gap '(reduce relative poverty) before you can even think about reducing absolute poverty. A maximum wage is a mechanism to achieve this aim. Assuming its an aim you consider worth supporting.
Your normal gripe with Corbyn is that he's not targeting issues that the public care about. But polling evidence shows there is public revulsion to excessive boardroom pay levels. By saying that Govt contracts will only be offered to companies that have a handle on boardroom pay levels (the 20:1 policy)he is at least focusing on an issue that the apparently public care about. As he did with the NHS and social care for the elderly, which the Tories are weak on.